全集 question

mingja

Dear Robert:

Sorry I have to write in English, not because I like it, but my chinese keyboard does not work and I cannot figure out what's wrong.  Anyway I have these 2 urgent questions from the 2002.12.09-2002.12.15

49. DS: 调查某网站受欢迎的程度，共有400人接受调查。其中说网站内容好的有185人，说网站速度快的有270人，问两种都没有说的。
（1）两者都说的有25人
（2）只说内容好的有160人
[确认]D
[思路]设说网站内容好的为A，说网站速度快的为B，接受调查的为全集I，即求(非A交非B)。由(非A交非B)等于(A并B)的补集，则先求(A并B)=A+B-(A交B)，由条件（1）得出185+270-25=430，超出I。由条件（2）可以得出同样的结果。

Question is: 由条件（1）or 条件（2）得出185+270-25=430，超出I。, and what does it mean.  Can you have a negative (非A交非B) ?  What does negative (非A交非B) mean?

Next questions:

100. 三个考官考30学生，A认为15名过，B认为17名过，C认为18名过。只有三人都过者才叫过，问至少有几人过了。
[讨论]5？

Aand B overlaps by 2
C overlaps A by 3, and C overlaps B by 5

So I thought at least only 2 passes.  

What is the correct method to calculate (AnB) given the question (or (BnC) or (AnC) for that matter)?

For example if say a question ask: There are a total of 200 household, with or without TV or phone or both  or none.  Given 60% have TV (T), and 70% have phone (P), what is (TnP), what is (Not T n Not P)?


Thanks a lot!

kitten369

for 100)

I don't think the answer is right. my answer is 0.

Because If we guess everyone in this class pass 2 exam, then there will be 30*2 in total, then 60> 15+17+18 so at least 0 pass.
in other word, A and B overlaps by 2, then for the member in C, they distribute into the 30-2 (which only pass 1 exam) so there will on one pass